1. Field of the Invention
The present invention relates to a high-frequency choke coil, and more particularly, to a high-frequency choke coil used for removing high-frequency noise radiated from and entering electronic equipment and similar devices.
2. Description of the Related Art
Up to now, in order to improve the high-frequency characteristic of a high-frequency choke coil, a method for suppressing stray capacitance of the coil conductor and for making the frequency characteristic of the magnetic core better by improving the quality of the magnetic core material at the same time has been used. Alternatively, a method for obtaining a high impedance by increasing the number of turns of the coil conductor and for compensating for the low relative magnetic permeability has been used.
However, even if the quality of the magnetic core material is improved, there is a problem that the relative magnetic permeability is decreased and a high impedance can not be obtained in a high-frequency range because the frequency characteristic of ferrite as a magnetic core material exhibits a phenomenon called "Snoek limit."
Also, when the decreased relative magnetic permeability in a high-frequency range is compensated by increasing the number of turns of a coil conductor, the stray capacitance is increased to generate an LC resonance. That is, if this method is relied on, the impedance is made high at a resonance frequency, but the Q factor also becomes high. Consequently, the insertion loss of the high-frequency choke coil is decreased. Moreover, because the resonance frequency is varied because of inductance and capacitance components distributed around the high-frequency choke coil, it has been inappropriate to apply this method to a choke coil.